A report in The Wall Street Journal claims that Samsung's Galaxy S5 flagship phone has performed below expectations. The S5 is said to have sold 12 million units in its first three months on sale; roughly 4 million fewer than its predecessor and overall around 40 percent fewer than projected. Sales were said to be down over 50 percent in China, with the US as the only major market where sales actually increased. The US is, however, Samsung's biggest market.

Samsung reportedly overestimated how much stock would be needed, leading to an increased advertising spend to get rid of units that were "piling up in warehouses." Last month the company promised to "fundamentally reform" its smartphone portfolio after reporting plummeting profits and revenue.The Journal also cites sources that believe Samsung is considering making some changes at the executive level — with mobile chief co-CEO JK Shin possibly ceding his role to fellow co-CEO in charge of TVs and appliances — but these rumors are cagier, and the plans are said to be far from final.Any management shake-up would come as Samsung faces frenzied speculation over the company's top level of leadership. Chairman Lee Kun-hee, the man who orchestrated Samsung's meteoric rise in the '90s and beyond, has been seriously ill after suffering a heart attack in May and, while his son Jay Y. Lee is considered near-certain to take over the role at some point, the company has been silent on any succession plan.A Samsung spokesperson said "We don't comment on rumors and speculation" when contacted by The Verge.